Polymer blends with improved hydrolytic stability

ABSTRACT

This invention relates to polymer blends having improved hydrolytic stability which comprise, in admixture, (1) a linear aromatic polyester of monomer residues consisting essentially of residues of a dicarboxylic acid and a bisphenol, and (2) a SAN polymer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending U.S. patentapplication Ser. No. 193,052, filed Oct. 2, 1980, now abandoned, whichin turn, is a continuation of U.S. patent application Ser. No. 90,179,filed Nov. 1, 1979, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to blends of a SAN polymer and a linear aromaticcarboxylic polyester of monomer components consisting essentially of abisphenol and a dicarboxylic acid wherein the dicarboxylic acid can bean aromatic dicarboxylic acid or an aliphatic saturated dicarboxylicacid such as oxalic or adipic acids.

Linear aromatic polyesters prepared from aromatic dicarboxylic acids andbisphenols are well known for their suitability for molding, extrusion,casting, and film-forming applications. For example, U.S. Pat. No.3,216,970 to Conix, discloses linear aromatic polyesters prepared fromisophthalic acid, terephthalic acid, and a bisphenolic compound. Suchhigh molecular weight compositions are known to be useful in thepreparation of various films and fibers. Further, these compositions,when molded into useful articles using conventional techniques, provideproperties superior to articles molded from other linear polyestercompositions. For instance, aromatic polyesters are known to have avariety of useful properties, such as good tensile, impact, and bendingstrengths, high thermal deformation and thermal decompositiontemperatures, resistance to UV irradiation and good electricalproperties.

In order to form a successful molding resin on a commercial scale, apolymer should be capable of being molded conveniently withoutsignificant degradation in physical properties. In this respect,although the aforementioned aromatic polyesters generally displayexcellent physical and chemical properties, a persistent and troublesomeproblem has been their sensitivity to hydrolytic degradation at elevatedtemperatures. This is demonstrated by the loss of tensile strength whichcan occur when an aromatic polyester resin is molded and subsequentlyimmersed in boiling water. This tendency may be explained, in part, bythe hydrolysis of the ester linkages under these conditions. In anyevent, it is to be appreciated that sensitivity to moisture represents asignificant problem in aromatic polyester resins that wouldsignificantly limit their commercial utility in applications such as inautoclaves or an elevated temperatures in humid atmospheres.

Accordingly, it is a principal object of this invention to preparearomatic polyester compositions having superior physical and chemicalproperties as well as improved hydrolytic stability.

SUMMARY OF THE INVENTION

It has now been found that thermoplastic polyester molding compositionshaving improved hydrolytic stability may be prepared by blending alinear aromatic polyester consisting essentially of bisphenol anddicarboxylic acid monomer components with a SAN polymer additive, i.e. apolymer consisting essentially of styrene or alpha-alkyl styrene andacrylonitrile or alpha-alkyl-acrylonitrile monomer components. Thepreferred aromatic polyesters of this invention consist essentially of abisphenol component and at least one aromatic dicarboxylic acidcomponent, most preferably selected from the group consisting ofisophthalic acid, terephthalic acid, or mixtures thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The linear aromatic polyesters of the present invention can convenientlybe prepared by condensing a diacid halide, e.g. a diacid bromide orespecially a diacid chloride of a dicarboxylic acid, dissolved in anorganic liquid which is a solvent for the polyester to be formed, with ametal phenolate of a bisphenol, dissolved in a liquid which isimmiscible with the solvent for the diacid halide. This interfacialpolymerization process is more fully described in U.S. Pat. No.3,216,970, to Conix, the disclosure of which is incorporated herein byreference. The foregoing interfacial polymerization method is amodification of the solution polyesterification process which can alsobe employed in the preparation of suitable aromatic polyesters from theaforementioned diacid halide and the bisphenol. Such solutionpreparatory procedures are disclosed in P. W. Morgan "CondensationPolymers by Interfacial and Solution Methods", Interscience Publishers,1965, Chapter VIII, particularly pages 332-364, the disclosure of whichis incorporated herein by reference.

The bisphenols which can be used in this process are known in the artand correspond to the general formula: ##STR1## where Ar is aromatic,preferably containing 6-18 carbon atoms (including phenyl, biphenyl andnaphthyl); G is alkyl, haloalkyl, aryl, haloaryl, alkylaryl,haloalkylaryl, arylalkyl, haloarylalkyl, cycloalkyl, or halocycloalkyl;E is a divalent (or di-substituted) alkylene, haloalkylene,cycloalkylene, halocycloalkylene, arylene, or haloarylene, --O--, --S--,--SO--, --SO₂ --, --SO₃ --, --CO--, ##STR2## T and T' are independentlyselected from the group consisting of halogen, such as chlorine orbromine, G and OG; m is an integer from 0 to the number of replaceablehydrogen atoms on E; b is an integer from 0 to the number of replaceablehydrogen atoms on Ar, and x is 0 or 1. When there is plurality of Gsubstituents in the bisphenols, such substituents may be the same ordifferent. The T and T' substituents may occur in the ortho, meta orpara-positions with respect to the hydroxyl radical. The foregoinghydrocarbon radicals preferably have carbon atoms as follows: alkyl,haloalkyl, alkylene and haloalkylene of 1 to 14 carbons; aryl, haloaryl,arylene and haloarylene of 6 to 14 carbons; alkylaryl, haloalkylaryl,arylalkyl and haloarylalkyl of 7 to 14 carbons; and cycloalkyl,halocycloalkyl, cycloalkylene and halocycloalkylene of 4 to 14 carbons.Additionally, mixtures of the above described bisphenols may be employedto obtain a polymer with especially desired properties. The bisphenolsgenerally contain 12 to about 30 carbon atoms, and preferably 12 toabout 25 carbon atoms.

Typical examples of bisphenols having the foregoing formula includebisphenol-A; i.e. bis(4-hydroxyphenyl)-2,2-propane,bis(3-hydroxyphenyl)-1,2-ethane, bis(4-hydroxyphenyl)-1,2 ethane as wellas the other bisphenols illustrated in G. Salee, U.S. Pat. No. 4,126,602(issued Nov. 21, 1978) at column 2, line 68-column 3, line 47, thedisclosure of said patent being incorporated herein reference.Representative bisphenols include p,p'-biphenol, and the other biphenolsillustrated in the aforementioned U.S. Pat. No. 4,126,602, at column 3,lines 47-55. Mixtures of isomers of the foregoing bisphenols andbiphenols can be used. Preferably, the bisphenol component, i.e. thebisphenol monomer residue, of the present polyester is derived frombisphenol-A.

The dicarboxylic acids which are useful in this process are also wellknown and can be represented by the formula: ##STR3## in which X isoxygen or sulfur, Z is alkylene, --Ar-- or --Ar--Y--Ar-- where Ar hasthe same definition as given with respect to the bisphenol, Y is analkylene of 1 to 10 carbons, haloalkylene, --O--, --S--, --SO--, --SO₂--, --SO₃ --, --CO--, ##STR4## and n is 0 or 1.

Suitable dicarboxylic acids include aromatic dicarboxylic acids such asisophthalic acid and terephthalic acid, as well as the other aromaticdicarboxylic acids illustrated in the aforementioned U.S. Pat. No.4,126,602 at column 4, lines 5-17.

Suitable aliphatic acids include oxalic acid, malonic acid,dithiomethonic acid and the other aliphatic dicarboxylic acidsillustrated in the aforementioned U.S. Pat. No. 4,126,602 at column 4,lines 17-19. Aromatic acids are preferred. Of the aromatic dicarboxylicacids, isophthalic acid and terephthalic acid are especially preferreddue to their availability and low cost. Most preferably, thedicarboxylic acid component comprises a mixture of about 75 to about 100mol percent isophthalic acid and about 25 to about 0 mol percentterephthalic acid.

When the dicarboxylic acids used in preparing a polyester of theinvention consist of both isophthalic and terephthalic acids inaccordance with an especially preferred embodiment of the invention, aweight proportion of isophthalic to terephthalic acid residues in thepolyester ranging from about 75:25 to about 90:10 provides an especiallysatisfactory result.

The polyester component of the invention are preferably prepared by atransesterification polymerization which is generally carried out in themelt, i.e. without use of a reaction diluent. Such transesterificationpolymerization reactions involve an ester interchange reaction between(1) a di-lower alkanoyl ester of the bisphenol (for example a diester ofa bisphenol and a lower, i.e. C₁ -C₆ alkanoic acid such as acetic acid)and the dicarboxylic acid; (2) said di-lower alkanoyl ester of thebisphenol and a di-lower alkyl ester of the dicarboxylic acid, e.g. adimethyl ester of said dicarboxylic acid; and (3) the bisphenol and adiaryl ester of the dicarboxylic acid wherein said ester is the diesterof the dicarboxylic acid and a monohydroxy aromatic compound of thebenzene or naphthalene series of 6-20 carbon atoms such as phenol (asdescribed in U.S. application Ser. No. 45,464 of J. C. Rosenfeld, filedJune 4, 1979, the disclosure of which is incorporated herein byreference). The aforementioned transesterification reaction routes forpreparation of the present polyester are more particularly described inT. Maruyama et al., U.S. Pat. No. 4,075,173, issued Feb. 21, 1978, thedisclosure of which is incorporated herein by reference.

It is especially preferred to employ in the invention, polyestersprepared by transesterification reaction of the bisphenol and a diarylester of the dicarboxylic acid, i.e. prepared by transesterificationreaction route (3) above. Preparation of the polyester by the latterespecially preferred transesterification reaction is more particularlydescribed in British Pat. No. 924,607, published Apr. 24, 1963, (toImperial Chemical Industries Ltd.); K. Eise et al., German PreliminaryApplication No. 22 32 877, published Jan. 17, 1974; G. Bier, Polymer 15527-535 (1974); G. M. Kosanovich and G. Salee, U.S. patent applicationsSer. No. 128,742, filed Mar. 10, 1980 and Ser. No. 198,979, filed Oct.21, 1980; J. C. Rosenfeld, U.S. application Ser. No. 128,743, filed Mar.10, 1980; and J. A. Pawlak, J. C. Rosenfeld and G. Salee, U.S. patentapplication Ser. No. 198,980, filed Oct. 21, 1980, the disclosures ofthe foregoing patent, article and applications being incorporated hereinby reference.

THE SAN POLYMER COMPONENT

The SAN polymer additive of the present composition is a known genus ofpolymer consisting essentially of a styrenic monomer component,including styrene as well as an alpha-lower alkyl-substituted styrene ormixtures thereof and an acrylonitrilic monomer component includingacrylonitrile as well as an alpha-lower alkyl substituted acrylonitrileor mixtures thereof. By lower-alkyl is meant a straight or branchedchain alkyl group of 1 to 4 carbon atoms exemplified by the methyl,ethyl, isopropyl and t-butyl groups. In readily available SAN polymers,the styrene component is generally styrene, alpha-straight chain alkylsubstituted styrene, typically alpha-methyl-styrene, or mixtures thereofwith styrene being preferred. Similarly in the readily available SANpolymers, the acrylonitrile component is generally acrylonitrile,alpha-methyl-acrylonitrile or mixtures thereof with acrylonitrile beingpreferred.

In the SAN polymer the styrene component is present in a major weightproportion, i.e. in a weight proportion of greater than 50%, typicallyabout 65% to about 90%, especially about 70% to about 80%, based on thecombined weight of the styrene component and the acrylonitrilecomponent. The acrylonitrile component is present in a minor proportion,i.e. in a weight proportion of less than 50%, typically about 10% toabout 35% especially about 20% to 30% based on the combined weight ofthe styrene monomer component and the acrylonitrile monomer component.

The SAN polymer class is more particularly identified and described inR. E. Gallagher, U.S. Pat. No. 3,988,393, issued Oct. 26, 1976(especially at Column 9, lines 14-16 and in Claim 8), in "Whittington'sDictionary of Plastics", Technomic Publishing Co., First Edition, 1968,page 231, under the section headed "Styrene-Acrylonitrile Copolymers(SAN)", and R. B. Seymour, "Introduction to Polymer Chemistry",McGraw-Hill, Inc., 1971, page 200, (last two lines) to page 201 (firstline). The preparation of a SAN polymer by copolymerization of styreneand acrylonitrile is more particularly described in the "Encyclopedia ofPolymer Science and Technology", John Wiley and Sons, Inc., Vol. 1,1964, pages 425-435.

The disclosures of the foregoing references which describe SAN polymersand the preparation thereof are incorporated herein by reference.

Proprietary SAN polymer compositions include Blendex 586, a polymer ofstyrene, alpha-methyl styrene and acrylonitrile monomers containing aminor weight proportion (about 27.5%) of the acrylonitrile monomer whichis manufactured by Borg-Warner Chemicals. Other proprietary SAN polymercompositions include compositions manufactured under the designation"Tyril" by the Dow Chemical Co., such as Tyril 860, Tyril 867, Tyril 870and Tyril 880, compositions manufactured under the designation "Lustran"by Monsanto Corporation as well as compositions manufactured under thedesignations C-11, RMD 4511; C-11, RMD 4520; C-11, RMD 4400; and C-11,RMDA 4420 by Union Carbide Corporation. Use of the aforementionedproprietary Tyril compositions as the SAN polymer component of theinvention, especially Tyril 860, provides an especially good result inthe practice of the invention.

Most preferably, the polymeric additive in the present polyester-SANpolymer compositions consists essentially of a SAN polymer, i.e. thepresent polyester-SAN polymer blend composition is preferably a binarymixture of the SAN polymer and the polyester.

The novel resin compositions of the instant invention are prepared byblending the linear aromatic polyester with the SAN polymer insubstantially molten condition. The blending or mixing process can beperformed using conventional mixing equipment such as, for example, aBanbury mixer, mixing roll, kneader, screw extruder, or injectionmolding machine.

Although the mixing ratio may vary depending on the physical propertiesdesired in the resultant polymer blend, the SAN polymer is generallypresent in a proportion of about 1 to about 99 weight percent based onthe weight of the admixture of the polyester and the SAN polymer.

It is preferred that the SAN polymer component be in a minor weightproportion, i.e. of less than 50 weight percent, based on the combinedweight of the polyester and SAN polymer. More preferably, the SANpolymer is present in a proportion of about 1 to about 30 weight parts,per 100 parts of the SAN polymer and the polyester mixture. Use of theSAN polymer in a proportion of about 1 to about 15 weight parts per 100parts of the mixture is especially desirable to obtain a composition ofthe invention of exceptionally enhanced impact resistance.

The novel polymer compositions of the present invention may also includevarious additives such as organic or inorganic fillers, stabilizers,antistatic agents, and flame retardants.

The halogen-containing flame retardant agents of U.S. application Ser.No. 863,556 of G. Salee, filed Dec. 22, 1977, issued on July 8, 1980 asU.S. Pat. No. 4,211,687, and of copending U.S. application Ser. No.863,381 of G. Salee, also filed Dec. 22, 1977, now U.S. Pat. No.4,251,429, issued Feb. 17, 1981 can be employed in the presentcompositions. The disclosures of these applications are incorporatedherein by reference.

The additive-containing resin mixture of the invention may be prepared,if desired, by charging the polyester and the SAN polymer with theadditive to a conventional mixing apparatus, such as a premix mixer, ormelt extruder. The resultant additive-containing composition can then bemolded directly in an injection molding apparatus of an extruder. Themolded articles thus formed have excellent hydrolytic stability andtensile strength.

The fillers which may be employed in the invention are preferablyparticulate fillers such as particulate glass (e.g. chopped glass fiber,glass rovings, glass microballons or microspheres and pulverulentglass), particulate clay, talc, mica, inorganic natural fibers,synthetic organic fibers, alumina, graphite, silica, calcium carbonate,carbon black, magnesia and the like. Generally, such fillers are addedto reinforce the structural integrity of a polymer, e.g. to inhibitsagging and/or to improve the tensile strength and stiffness of thepolymer composition and also to reduce shrinkage, minimize crazing,lower material costs, impart color or opacity, and improve the surfacefinish of the polymer composition. Generally, the amount of particulatefiller employed in the compositions of the invention is in the range ofabout 5 to about 70 weight percent, preferably about 5 to about 40weight percent, and especially about 8 to about 30 weight percent basedon the combined weight of the polyester and the SAN polymer additive.The filler employed is preferably inorganic.

According to the invention, use of a particulate glass filler,advantageously glass fibers, is especially desirable.

The glass filler, especially glass fiber filler, employed in theinvention preferably contains an organic coupling agent as a very thincoating on the glass particles. The coupling agent forms an adhesivebridge between the glass and the polymer blend thereby enhancing thestrength properties of the filled polymer blend. Typically, organiccoupling agents employed in the art include transition metal complexesof unsaturated aliphatic acids such as the methacrylato chromic chloridecomplex as well as various organic silane compounds including vinyltrichlorosilane, as well as the other exemplified silane coupling agentslisted in copending U.S. patent application of G. Salee, Ser. No.905,623, filed May 12, 1978, now abandoned, copending continuationthereof, filed May 28, 1980, as U.S. application Ser. No. 154,174, nowU.S. Pat. No. 4,284,549, issued May 28, 1980 the disclosure of which isincorporated herein by reference.

Preferably, the coupling agent employed with the glass filler accordingto the invention is a silane coupling agent.

Glass fillers are frequently manufactured and sold so as to contain thecoupling agent as a proprietary ingredient on the surface of the glass.The coupling agents and their use with glass fillers are discussed inmore detail in W. V. Titow and B. J. Lanham, "ReinforcedThermoplastics", Halstead Press, 1975, pages 83-88 and L. Mascia, "TheRole of Additives in Plastics", J. Wiley and Sons, 1974, pages 89-91,the disclosures of which references are incorporated herein byreference.

The present blends have utility as engineering thermoplastics inmanufacture of automotive parts as well as housings and casings ofelectrically operated apparatus such as radios and power tools, forexample, drills and saws. On account of the enhanced hydrolyticstability of the present blends, the present compositions are alsouseful for manufacture of household wares designed for exposure tomoisture at elevated temperatures such as dishes, particularly ovenware, and the handles and covers of coffee and tea pots.

The following examples further illustrate the various aspects of theinvention but are not intended to limit it. Various modifications can bemade in the invention without departing from the spirit and scopethereof. Where not otherwise specified in this specification and claims,temperatures are given in degrees centigrade, and all parts andpercentages are by weight.

EXAMPLE 1 (Control)

A bisphenol-A-isophthalate-terephthalate polyester is prepared byreaction of the bisphenol with diacid halides of isophthalic acid andterephthalic acid as follows:

A mixture of 21,636 grams (94.74 moles) of bisphenol-A, 16,565 grams(81.60 moles) of isophthaloyl chloride, 20,924 grams (14.4 moles) ofterephthaloyl chloride, 380 grams (2.153 moles) of paratertiary butylphenol, and 515 pounds of methylene chloride solvent are charged under ablanket of dry nitrogen gas to a dry 100 gallon reaction vessel equippedwith agitation means. To a 50 gallon addition vessel is charged 20,067grams (198.31 moles) of triethylamine catalyst. The triethylamine isadded gradually at a temperature of 10° to 20° to the agitated reactionmixture from the addition vessel over a period of 3 hours and 25 minutesunder a blanket of dry nitrogen.

The 50-gallon addition vessel is then rinsed with 250 pounds ofmethylene chloride and the methylene chloride rinse is added to thereaction mixture in the polyesterification reaction vessel. Agitation ofthe reaction mass is continued for 3 hours at about 20°. Then a mixtureof 600 ml of concentrated aqueous hydrochloric acid dissolved in 15gallons of deionized water is stirred into the reaction mixture. Thereaction mass is allowed to stratify into an upper aqueous layer and alower organic layer containing the polyester product. The lower organiclayer is withdrawn and then washed free of chloride ion with deionizedwater.

The resulting organic layer is divided into two equal portions.Isopropyl alcohol (190 pounds) is added to each portion to precipitatethe polyester. On completion of the addition methylene chloride solventis removed by distillation. During the distillation an additional 60pounds of isopropyl alcohol is added to each portion to insure completeprecipitation of the polyester product. The precipitated polyesterproducts are recovered from each isopropyl-alcohol containing distillantportion, combined and dried to obtain an excellent yield of a lineararomatic polyester of bisphenol-A, isophthalic acid and terephthalicacid having a mole ratio of terephthaloyl monomer residues toisophthaloyl monomer residues of about 15:85. The polyester product hasan intrinsic viscosity of 0.58 dl/g as determined at a temperature of30° at a concentration of 0.5% in a symmetrical tetrachloroethanesolution of the polyester.

The polyester made by the foregoing solution polymerization preparatoryprocedure, after being dried at 120° for four hours, is compacted byextrusion from a Haake extruder operating under the followingconditions:

    ______________________________________                                        TEMPERATURE OF                                                                       Zone   Zone   Zone Zone                                                RPM    1      2      3    4    Die Melt                                                                             Torque Amp.                             ______________________________________                                        90     290°                                                                          290°                                                                          290°                                                                        290°                                                                        310°                                                                          4000-  75                                                                     5000m.-g.                               ______________________________________                                    

The compacted extruded polyester strands are chopped into pellets whichare dried and injection-molded into specimens suitable for evaluation ofproperties, e.g. tensile properties, in an Arburg Injection MoldingApparatus MOdel 221E/150 operating under the following conditions:

    ______________________________________                                        Cylinder Temperature                                                                            620° F.                                              Mold Temperature  250° F.                                              Molding Pressure  17,760 psi                                                  ______________________________________                                    

The heat distortion temperature at 264 psi, i.e. HDT, the Notched Izodimpact resistance, the tensile strength and tensile modulus of themolded polyester are measured and these data are presented with theforegoing injection molding conditions in the Table below. Additionalspecimens of the injection molded polyester are immersed in a bath ofboiling water of substantially neutral pH for one week. After beingraised from the bath these specimens are tested for tensile modulus andtensile strength which data is also presented in Table I below.

EXAMPLE 2

A physical mixture of 240 parts of the dry linear aromatic polyester ofExample 1 and 30 parts of a proprietary SAN polymer manufactured by DowChemical Corp. under the designation Tyril 860 are compacted, injectionmolded and tested for properties substantially as described in Example 1above except that additionally a portion of the specimens of this blendare allowed to remain in boiling water for two weeks and are then testedfor tensile strength and modulus properties. The injection moldingcompositions and the properties of the resulting polyester-SAN polymerblend which contains about 11% of the SAN polymer, based on the combinedweight of the polyester and the SAN polymer are presented in Table Ibelow.

EXAMPLE 3

The procedure of Example 2 is repeated substantially as described abovein preparing and injection molding a blend employing 600 parts of thepolyester and 75 parts of the SAN polymer (corresponding to about thesame proportion of the SAN polymer as in Example 2) omitting the secondweek of immersion of the molded blend in boiling water. The results ofthis Example are presented in Table I below.

EXAMPLE 4

The procedure of Example 2 is repeated substantially as described inpreparing and testing a blend containing about 25% of the SAN polymeradditive and about 75% of the polyester except that boiling waterimmersion is omitted. An excellent blend according to invention isobtained. The results of this Example are also presented in Table Ibelow.

EXAMPLE 5

A glass fiber filled blend of a linear aromatic polyester and SANpolymer additive is prepared employing 240 parts of the linear aromaticpolyester of Example 1, 30 parts of the SAN polymer additive of Example2 (corresponding to about 11% of this additive based on the SAN polymerand polyester components of the blend) and 30 parts of a proprietarychopped glass fiber (3/16-inch length) as reinforcement fillercontaining a proprietary silane coupling agent, said proprietary glassfiller being manufactured under the designation 419AA by the OwensCorning Fiberglass Company. The preparatory procedure employed in thisExample is substantially that of the preceding Example with theexception that, to insure homogeneous distribution of the glass fiberfiller in the product, the initially obtained injection molded filledproduct is ground, dried and remolded in the injection moldingapparatus. There is obtained an excellent filled blend in accordancewith the invention. The results of this Example are also tabulated inTable I below.

                                      TABLE I                                     __________________________________________________________________________                            Example 1                                                                     (Control)                                                                           Example 2                                                                           Example 3.sup.(a)                                                                    Example 4                                                                           Example                      __________________________________________________________________________                                                     5.sup.(a,b)                  Bisphenol Polyester (%) 100%  89%   89%    75%   89%                          SAN Polymer Additive (%)                                                                              None  11%   11%    25%   11%                                                        (Tyril                                                                              (Tyril (Tyril                                                                              (Tyril                                                     860)  860)   860)  860)                         Injection Molding Conditions                                                  Cylinder Temperature (°F.)                                                                     620°                                                                         560°                                                                         580°                                                                          570°                                                                         570°                  Mold Temperature (°F.)                                                                         250°                                                                         250°                                                                         250°                                                                          250°                                                                         240°                  Injection Pressure, psi 17,760                                                                              15,440                                                                              13,320 7,770 14,430                       Properties                                                                    HDT at 264 psi          162.3°                                                                       154.4°                                                                       --     119.6°                                                                       167°                  Notched Izod Impact Resistance,                                               ft. lbs/in.             6.1   14.8  --     1.2   1.67                         Tensile Properties Prior to Immersion                                         Tensile Strength psi    9,700  9,821                                                                               9,898 --    13,307                       Tensile Modulus, psi × 10.sup.-5                                                                3.0   3.44  3.69   --    6.22                         After One (1) Week Immersion in Boiling Water                                 Tensile Strength, psi   3,800 10,319                                                                              10,015 --    --                           Tensile Modulus, psi × 10.sup.-5                                                                 3.27 3.37  3.65   --    --                           After Two (2) Weeks Immersion in Boiling Water                                Tensile Strength, psi   --    10,803                                                                              --     --    --                           Tensile Modulus, psi × 10.sup.-5                                                                --    5.23  --     --    --                           __________________________________________________________________________     NOTES TO TABLE I                                                              .sup.(a) The molded product blends of Examples 3 and 5 are also tested fo     percent elongation. The percent elongation (yield) of these products are:     Example 3: 6.6%, prior to boiling water immersion; 5.7%, after immersion;     Example 5: 3.7%;                                                              .sup.(b) The molded product blend of Example 5 contains about 11% glass       fiber based on the combined weight of the polyester and the SAN polymer       components of the blend.                                                 

Comparison of the product tensile strengths of the pure molded polyesterin Control Example 1, prior to, and subsequent to immersion in boilingwater with the corresponding product tensile strengths in the Examples 2and 3 which describe blends of the SAN polymer additive and thecorresponding polyester indicate the unexpected enhancement inhydrolytic stability achieved by blending the polyester with the SANpolymer according to the invention.

For example, the percentage loss in tensile strength of the polyester ofControl Example 1 on one week immersion in boiling water is more thanabout 60%.

In unexpected contrast to this result, the products of Examples 2 and 3(containing about 11 weight percent of SAN polymer additive blended withsaid polyester) exhibit substantially no loss in tensile strength on oneweek immersion in boiling water. The product blend of Example 2 evenretains substantially all of its original tensile strength on a two weekimmersion in boiling water.

EXAMPLE 6 (Control)

A bisphenol-A-isophthalate-terephthalate polyester is prepared by asemi-continuous transesterification procedure as follows:

Mixtures of a 75/25 diphenyl isophthalate/diphenyl terephthalate mixtureand bisphenol-A were vacuum oven-dried for about 3 hours at 2 mm Hg inlarge flat trays then weighted into polyethylene-lined 5-gallon pailsand sealed until used.

The proportions used of the bisphenol and diaryl ester mixture areinitially 16.25 kg (3.7 moles) and 16.33 moles (5.2 moles),respectively, providing a mole percent excess of the diaryl esterreactant over the bisphenol of about 0.5%. Later in the reaction, theproportions of the reactants are adjusted to provide a mole percentexcess of the diaryl ester of about 0.75 mole percent over the bisphenoland still later, the proportions of reactants are adjusted to providediaryl ester in a mole percent excess of about 1.0% over the bisphenol.

The diphenyl isophthalate, diphenyl terephthalate, and bisphenol-A arecharged to a stainless steel melt tank and melted at about 180° C. undera blanket of dry nitrogen. The molten monomer mixture is transferred viaheated lines to a continuously stirred oil heated reactor. Catalyst(potassium phenoxide, 0.041 molar solution in phenol, 0.0081 moles, i.e0.05 mole percent based on bisphenol-A) is added. Vacuum is applied andthe temperature (which is initially 220°) is raised gradually. Afterabout 2.5 hours, the pressure is about 70 mm and the temperature is 280°C. Intrinsic viscosity of the polyester prepolymer at this point isabout 0.17 dl/g.

The prepolymer is transferred via heated lines to a second stirredreactor and another prepolymer is prepared similarly to the firststirred reactor.

The prepolymer from the second stirred reactor is fed continuously atabout 20-25 lbs/hour to a vertical wiped thin film reactor which ismaintained at an internal temperature of 300° C. and a pressure of 1.50mm Hg (abs.). The reaction mass fed to the top of the wiped thin filmreactor flows down through the reactor propelled by gravity and by thedownward thrust of the pitched rotor blades. These blades also agitateand renew the polymer on the heated reaction surface of the thin filmreactor. The material leaving the thin film reactor has an intrinsicviscosity of about 0.4 dl/g.

The polymer is pumped out from the bottom of the wiped thin film reactorand fed to a 5-stage twin screw horizontal extruder having five vacuumvenst (one from each stage). The extruder is operated at about 0.8 mm Hg(abs.) pressure, and a screw speed of 125 rpm. The pressure ismaintained uniformly throughout the barrel, i.e. through the extruder.The temperature of the melt in the different stages of the extruder ismaintained between about 320° C. and about 340° C., the formertemperature being the melt temperature at the feed end of the extruderand the latter temperature being the melt temperature at the outlet endof the extruder. The aforementioned melt temperature profile within theextruder is controlled by maintaining the following three temperaturezones on the outside of the extruder barrel: Zone 1 (near the feed endof the extruder): 305° C.; Zone 2 (near the mid-section of theextruder): 310° C.; Zone 3 (near the outlet end of the extruder): 315°C. Under these operating conditions, light yellow, clear, tough polymeris produced at a rate of 20 lbs/hour. The product has an intrinsicviscosity of about 0.60 dl/g.

The polyester made by the foregoing melt transesterificationpolymerization preparatory procedure, after being dried for about 16hours is compacted by extrusion from a Haake extruder operating underthe following conditions:

    ______________________________________                                        TEMPERATURE OF                                                                       Zone   Zone   Zone Zone                                                RPM    1      2      3    4    Die Melt                                                                             Torque                                                                              Amp.                              ______________________________________                                        50     360°                                                                          360°                                                                          340°                                                                        340°                                                                        350°                                                                          11,000                                                                              40                                                                      m.-g.                                   ______________________________________                                    

The compacted extruded polyester strands are chopped into pellets whichare dried and injected molded into sample specimens suitable forevaluation of properties, e.g. tensile properties, on an ArburgInjection Molding Apparatus Model 221E/150, operating under thefollowing conditions:

    ______________________________________                                        Cylinder Temperature                                                                            600° F.                                              Mold Temperature  250° F.                                              Molding Pressure  14,430 psi                                                  ______________________________________                                    

The tensile strength of the molded polyester is measured and this datais presented with the foregoing injection molding conditions in Table IIbelow. Additional specimens of the injection molded polyester areimmersed in a bath of boiling water of substantially neutral pH for oneand two weeks. After being raised from the bath, these specimens weretested for tensile strength. This data is also presented in Table IIbelow.

EXAMPLE 7

A physical mixture of 240 parts of the dry transesterification preparedlinear aromatic polyester of Example 6 and 30 parts of the SAN polymerof Example 2 are compacted, injection molded and tested for propertiessubstantially as described in Example 6 above. The injection moldingconditions and the properties of the resulting polyester-SAN polymerblend which contains about 11% of the SAN polymer, based on the combinedweight of the polyester and the SAN polymer, are presented in Table IIbelow.

                  TABLE II                                                        ______________________________________                                                           Example 6                                                                     (Control)                                                                             Example 7                                          ______________________________________                                        Bisphenol Polyester (%)                                                                            100%      89%                                            SAN Polymer Additive (%)                                                                           --        SAN                                                                           Polymer                                                                       of Ex. 2                                                                      (11%)                                          Injection Molding Conditions                                                  Cylinder Temperature (°F.)                                                                  600°                                                                             550°                                    Mold Temperature (°F.)                                                                      250°                                                                             250°                                    Injection Pressure, psi                                                                            14,430    13,320                                         Tensile Properties Prior to Immersion                                         Tensile Strength, psi                                                                              10,166    10,238                                         After One (1) Week Immersion in                                               Boiling Water                                                                 Tensile Strength, psi                                                                              427        2,918                                         After Two (2) Weeks Immersion in                                              Boiling Water                                                                 Tensile Strength, psi                                                                              203       749                                            ______________________________________                                    

EXAMPLE 8 (Control)

A linear aromatic polyester of bisphenol-A, isophthalic acid, andterephthalic acid in the proportions of the polyester of Example 6 isprepared by the semi-continuous melt transesterification procedure ofExample 11 of aforementioned U.S. application Ser. No. 128,742 is driedand then compacted by extrusion from a Haake extruder substantially asdescribed in Example 1.

The compacted extruded strands of polymeric composition are chopped intopellets which are dried and injected molded into sample specimenssuitable for evaluation of properties, e.g. tensile properties, on anArburg Injection Molding Apparatus Model 221E/150.

The tensile strength, percent elongation, notched Izod impact strengthand heat distortion temperature of the molded specimens are measured andare presented below in Table III. Additional specimens of the injectionmolded product are immersed in a bath of boiling water of substantiallyneutral pH for one, two and three weeks. After being raised from thebath, the specimens are tested for tensile strength and percentelongation. This data is also presented in Table III below.

EXAMPLE 9

A physical mixture of 1700 parts of the dry transesterification preparedlinear aromatic polyester of Example 8 and 300 parts of a proprietarySAN polymer of styrene, alpha methyl styrene and acrylonitrilemanufactured by Borg Warner Chemicals under the designation Blendex 586are dried, extrusion-compacted injection molded and tested forproperties substantially as described in Example 8 above. The measuredproperties of the resulting polyester-SAN polymer blend which containsabout 15 percent of the SAN polymer based on the combined weight of thepolyester and the SAN polymer are compared in Table III with thecorresponding properties of the polyester of Example 8.

                  TABLE III                                                       ______________________________________                                                           Example 8                                                                     (Control)                                                                             Example 9                                          ______________________________________                                        Bisphenol Polyester  100%      85%                                            SAN Polymer Additive --        15%                                                                           (Blendex                                                                      586)                                           Injection Molding Conditions                                                  Cylinder Temperature (°F.)                                                                  600°                                                                             590°                                    Mold Temperature (°F.)                                                                      250°                                                                             250°                                    Injection pressure (psi)                                                                           15,540    12,210                                         Properties Prior to Immersion                                                 Tensile Strength (psi)                                                                             10,142    10,346                                         Elongation (%)       7.4(Y)    6.9(Y)                                         Notched Izod Impact Strength                                                                       4.9       2.1                                            (ft. lbs./in.)                                                                Heat Distortion Temperature at 264 psi                                                             151°                                                                             141°                                    Properties After One Week Immersion                                           Tensile Strength (psi)                                                                              1,798    10,398                                         Elongation (%)       0.6(B)    5.3(B+Y)                                       Properties After Two Week Immersion                                           Tensile Strength (psi)                                                                             275        6,175                                         Elongation (%)       0.1(B)    2.1(B)                                         Properties                                                                    After Three Week Immersion                                                    Tensile Strength (psi)                                                                             --         1,688                                         Elongation (%)       --        0.5(B)                                         ______________________________________                                         Y = yield, B = break                                                     

The invention has been described in the above specification andillustrated by reference to specific embodiments in the illustrativeexamples. However, it is to be understood that these embodiments are notintended to limit the invention since changes and modifications in thespecific details disclosed hereinabove can be made without departingfrom the scope or spirit of the invention.

What is claimed is:
 1. A thermoplastic polymeric composition comprising,in admixture, (a) a linear aromatic polyester of monomer componentsconsisting essentially of a bisphenol and a dicarboxylic acid, and (b) aSAN polymer.
 2. The composition of claim 1 wherein said dicarboxylicacid has the formula: ##STR5## wherein Z is alkylene, --Ar-- or--Ar--Y--Ar-- where Ar is aromatic, Y is alkylene, haloalkylene, --O--,--S--, --SO₂ --, --SO₃ --, --CO--, ##STR6## wherein G is alkyl,haloalkyl, aryl, haloaryl, alkylaryl, haloalkylaryl, arylalkyl,haloarylalkyl, cycloalkyl or cyclohaloalkyl; and n is 0 or
 1. 3. Thecomposition of claim 2 wherein said dicarboxylic acid is an aromaticdicarboxylic acid.
 4. The composition of claim 3 wherein said aromaticdicarboxylic acid is selected from the group consisting of isophthalicacid, terephthalic acid, and mixtures thereof.
 5. The composition ofclaim 1 wherein said bisphenol has the formula: ##STR7## wherein Ar isaromatic, G is alkyl, haloalkyl, aryl, haloaryl, alkylaryl,haloalkylaryl, arylalkyl, haloarylalkyl, cycloalkyl, or cyclohaloalkyl;E is divalent alkylene, haloalkylene, cycloalkylene, halocycloalkylene,arylene, or haloarylene, --O--, --S--, --SO--, --SO₂ --, --SO₃ --,--CO--, ##STR8## T and T' are independently selected from the groupconsisting of halogen, G and OG; m is an integer from 0 to the number ofreplaceable hydrogen atoms on E; b is an integer from 0 to the number ofreplaceable hydrogen atoms on Ar, and x is 0 or
 1. 6. The composition ofclaim 5 wherein the bisphenol is bisphenol A.
 7. The composition ofclaim 3 wherein the polyester is a transesterification-preparedpolyester.
 8. The composition of claim 7 wherein the polyester isprepared by transesterification reaction of the bisphenol and a di-ester of the dicarboxylic acid and a monohydroxy phenolic compound ofthe benzene or naphthalene series of 6 to 20 carbon atoms.
 9. Thecomposition of claim 1 wherein said SAN polymer is essentially the onlypolymeric additive to the polyester.
 10. The composition of claim 1wherein the SAN polymer is a copolymer of styrene and acrylonitrile. 11.The composition of claim 1 wherein the SAN polymer is a copolymer ofstyrene, alpha-methyl styrene and acrylonitrile.
 12. The composition ofclaim 1 wherein the SAN polymer is present in an amount of from about 1to 99 parts by weight per 100 parts by weight of the mixture of thepolyester and the SAN polymer.
 13. The composition of claim 12 whereinthe SAN polymer is present in a minor weight proportion based on thecombined weight of the polyester and the SAN polymer.
 14. Thecomposition of claim 13 wherein the SAN polymer is present in an amountof from about 1 to about 30 parts per 100 parts by weight of themixture.
 15. The composition of claim 14 wherein the SAN polymer ispresent in an amount of from about 1 to about 15 parts per 100 parts byweight of the mixture.
 16. The composition of claim 1 which alsoincludes a filler material.
 17. The composition of claim 16 wherein saidfiller material is particulate glass.
 18. The composition of claim 17wherein the filler material is glass fiber present in an amount of about5 to about 70 weight percent based on the combined weight of thepolyester and the SAN polymer.
 19. The composition of claim 18 whereinthe glass fiber contains an organic coupling agent.
 20. The compositionof claim 19 whrein said organic coupling agent is a silane.
 21. Athermoplastic polymeric composition comprising, in admixture, (a) alinear aromatic polyester prepared by transesterification of monomerreactants consisting essentially of a bisphenol and a diphenyl ester ofan aromatic dicarboxylic acid, and (b) a SAN polymer.
 22. A process forimproving the hydrolytic stability of a linear aromatic polyester resinof component monomers consisting essentially of a bisphenol and adicarboxylic acid which comprises adding from about 1 to about 99 partsby weight of a SAN polymer per 100 parts by weight of the resin mixtureto said polymer.
 23. A molded article formed from the composition ofclaim
 1. 24. A molded article formed from the composition of claim 16.25. A molded article formed from the composition of claim
 19. 26. Amolded article formed from the composition of claim 21.